1. Field of the Invention
The present invention relates to semiconductor devices, and more particularly, to a semiconductor device and a method for fabricating the same.
2. Discussion of the Related Art
Recently, as high density semiconductor device packing progresses rapidly, various geometrical structures of the semiconductor device have also been drastically changed.
FIG. 1 illustrates a section of a related art memory having cells each with a transistor and a capacitor.
Referring to FIG. 1, a semiconductor device is provided with a semiconductor substrate 1 having a field region FR and an active region AR defined by an active cell isolation film 2. In the active region AR of the semiconductor substrate 1, there are a transistor 10 for selective switching of a charge flow and a capacitor 20 for storage of charges switched by the transistor 10, both of which are arranged related to each other.
The transistor 10 has a gate insulating film pattern 11, a gate electrode pattern 12, spacers 13, and source/drain diffusion layers 14, and the storage capacitor 20 has a storage dielectric film 21 and a storage electrode 22.
The storage dielectric film 21 and the storage electrode 22 of the capacitor 20 are formed in a trench in the semiconductor substrate 1, with a portion 22a of the storage electrode 22 exposed from a surface of the semiconductor substrate 1, so as to be in electrical contact with the source/drain diffusion layer 14.
However, the related art semiconductor device has the following problems. Although a device packing density has been enhanced by forming the capacitor in the trench of the semiconductor substrate in the active region AR, because the trench is formed in the active region, the capacitor is formed within an area of the active region AR of the semiconductor device. This imposes a limit on increasing the capacitance of the capacitor. Moreover, since there is a limit on the reduction of the active region AR of the semiconductor device, there is a limit on the fabrication of a high density semiconductor device package.
Of course, if a structure of the capacitor is changed from above trench structure to a stack type structure in which elements are stacked on the semiconductor substrate 1 (on the transistor), the problem of size increase of the active region AR can be reduced to a certain extent. However, a serious problem occurs in that an overall step height of the semiconductor device unnecessarily increases as much as the stacking height of the capacitor.